This invention relates to sharpeners for wooden pencils.
Manually operated and electrically powered pencil sharpeners are well known. When a pencil is inserted through a pencil-receiving opening of a pencil sharpener""s housing, the pencil enters a sharpening assembly which cuts an outer layer of wood to expose and sharpen an inner core of lead or graphite.
Some manual pencil sharpeners include a selector guide. The selector guide has several openings sized to correspond to pencils of different thicknesses, for example, a standard adult size pencil (approximately {fraction (5/16)} inch nominal size) or a larger diameter child size pencil (approximately {fraction (7/16)} inch nominal size). The various openings of the selector guide are positionable in alignment with the pencil-receiving opening. The selector guide maintains proper alignment of the pencil with the sharpening assembly during the sharpening process.
Various configurations of electric pencil sharpeners are known. A common electric pencil sharpener has a sharpening assembly including a rotary means rotatable by a motor and cutter means operatively carried by the rotary means so as to rotate in a direction opposite to a rotational direction of the rotary means. U.S. Pat. No. 4,054,164 to Kose et al. and U.S. Pat. No. 4,966,208 to Uang, the disclosures of which are incorporated herein by reference, disclose such sharpening assemblies. While such pencil sharpeners are easy to use, they can quickly cause excess wear and waste of the pencil, i.e., by oversharpening. This problem is particularly acute with children lacking experience, judgment, and/or adequate hand/eye coordination.
Some electric pencil sharpeners include a self-governing sharpening assembly including a mechanism for preventing excess wear and/or oversharpening of a pencil. U.S. Pat. No. 3,777,791 to Uchida and U.S. Pat. No. 4,601,316 to Verdi, the disclosures of which are incorporated herein by reference, disclose exemplary self-governing sharpening assemblies. The sharpening assembly disclosed by Uchida prevents oversharpening by moving the cutter means away from the pencil when the pencil has a sufficiently sharp point. The pencil sharpener is adjustable to vary the degree of sharpness of the pencil before the cutter means is moved away from the pencil. Uchida discloses a variety of complex pivot mechanisms for providing such adjustability. Each of these mechanisms adds undesirable parts and manufacturing costs. Additionally, such pencil sharpeners are incapable of sharpening pencils of various sizes, particularly large diameter children""s pencils.
What is needed is a pencil sharpener which includes a self-governing sharpening assembly and is capable of sharpening pencils of various sizes, as well as a simplified self-governing sharpening assembly.
The present invention provides a pencil sharpener having a self-governing sharpening assembly which is capable of sharpening pencils of various sizes. Additionally, the present invention provides a pencil sharpener having a simplified, economical self-governing sharpening assembly. In one embodiment, the pencil sharpener includes a safety mechanism which prevents operation of the pencil sharpener when the sharpener""s receptacle is removed and the sharpening assembly is exposed. These features make the pencil sharpener ideal for use by children.
A pencil sharpener according to the present invention includes a housing defining a pencil-receiving opening and a self-governing sharpening assembly mounted on the housing in alignment with the pencil-receiving opening for sharpening pencils. The pencil sharpener also includes a motor operatively connected to the sharpening assembly for driving the sharpening assembly. A selector guide is mounted on the housing. The selector guide defines a plurality of openings. Each of the openings is smaller than the pencil-receiving opening and has a unique size corresponding to one of a plurality of common pencil sizes. Each of the plurality of openings is selectively positionable in alignment with the pencil-receiving opening for aligning a pencil with the sharpening assembly.
A self-governing sharpening assembly in accordance with the present invention includes a blade-supporting shaft having a lower end and an upper end having a reduced diameter portion. A rotary blade and a pinion are carried co-axially on the shaft. The rotary blade has spiral cutting edges. A blade holder defines a conical cavity for receiving an end of a pencil therein and has a bearing lug defining a bearing opening rotatably supporting the upper end of the shaft. The blade holder is supported by the housing to be rotatable around an axis of the conical cavity. An annular ring gear is fixedly supported by the housing and meshes with the pinion. A drive shaft drives the blade holder around the axis. A stop is slidably mounted to the blade holder in alignment with the conical cavity. The stop is connected to the lower end of the shaft. A spring member is supported by the blade holder. The spring member engages the stop and biases the reduced diameter portion of the shaft away from the bearing lug of the blade holder. A pencil advanced into the conical cavity is sharpened by the rotary blade until the pencil is sufficiently sharpened, at which point the pencil moves the stop against the spring bias, causing the reduced diameter portion of the shaft to enter the bearing opening of the bearing lug. The reduced diameter portion of the shaft is sized relatively to the bearing opening to allow for pivotal movement of the shaft and the rotary blade away from the pencil under influence of centrifugal force produced by rotation of the blade holder around the axis of said conical cavity, thereby ceasing sharpening and preventing oversharpening and/or waste of the pencil.
Optionally, the pencil sharpener may include a receptacle removably matable with the housing for receiving pencil shavings discharged from the sharpening assembly and/or a switch mounted on the housing for engaging any pencil inserted into the pencil-receiving opening. The switch is operatively connected to the motor and the sharpening assembly for driving the sharpening assembly when the switch is activated by any pencil inserted into the pencil-receiving opening.